Honestly just think this is a problem created by the internet drastically changing our society.
To completely oversimplify, for the unlucky less attractive people dating has always been a sort of numbers thing, the more people they meet the more chances of clicking with someone on an emotional level.
The problem is that the internet has drastically changed all the "natural" ways people used to meet and we've never really resolved the fact that massive amounts of socialisation online has had the effect of removing socialisation in person where meeting people and making up these numbers would happen.
The best way to stop incels, is for them to stop being incels by meeting people and making those connections that ultimately leads to the celibate part stopping. The problem is that they do not, and that the internet has given them the power to meet as few people as possible and then to complain about it. Then they fester in their hateful spaces only making themselves more and more unattractive and hating the world.
I don't have a solution though, they need to meet more people, a lot more people, until they click with one. And the internet has moved a lot of people online instead of offline. I know pua types say that shit too but w/e I'm not advocating for the scum shit I'm just saying meeting more people definitely helps.
What were incels before the internet? Hermits?